Gear.



I. E. MOGRACKBN."

GEAR.

APPLICATION FILED APRA, 1913 PatentedMayIZ, 1914 WITNESSES E MZM m .KMA W ISAAC E. MCCRAOKEN, OF PITTSBURGH. .PENNSYLVAIIIA ZEEAR.

Specification. of Letters Patent.

Application filed lipril 4. 1813. Serial No. 753,865.

7? M! w/mm, it may concern:

Be it known that l, l'saao E. McCnaonnn, a resident oi Pittsburgh. in the eonnly of i'lrllegheny and State of l-ennsylvania, have invented a new and useful li'1n rovement in Gears. of which the following is a specitica t ion.

This invention relates to toothed. gearing.

The object oi the invention is to produce. a new and improved gear, whirh is noiseless in operation. in which the teeth on a pair of gears mesh progressively 't roin end to end. in whieh the teeth are of r; wing shape in eross section and are formed with a varying pres sure angle from end to end, and are stronger at their ends than in the median plane ot the gear.

Other t)l)jl3.til.\ of the invention are in Qart obvious and in part will appear more fully hereinafter. I

in the drawings l ignre 1 represents a plan View of. a gear embodying the invention; Fig; 2 is a cross section thereof on the line Fig. l; Fig.4; is an end view of the gea r from the left in Fig. l, and showing the same meshing with a rank; Fig. 4 is a plan view of the rack shown'in Fig. 3; Fig. 5 is an end view of a pair of meshing gears embodying the invention; Figs. 6 and 7 are detail views of the cutters used in forming the gear; and Figs. 8 and 9 are similar views of a pair of cutters of modified "form. t r

For many years attempts have been made to devise some substitute For the ordinary gear or pinion having li h which are straight'aml parallel to the axis of the gearand of the same ('ross se:tion from end to :end. Finch gears have a number of objeotions, among whirh are the following: The end portions of the teeth are tzhe weakest, and the teeth must, therefore, be made of a eross sect-ion from end to'end snoh that the ends of the teeth will stand-the greatest duty the gear is required to hear. The middle portions of the teeth must therefore, be made heatier and stronger than is necessary. Some attempts hare been made to strengthen the teeth by sin-milling, but this expedient. ran only he adopted completely atboth ends ot' one ot' the gears or at one end of each gear, and only ineompletely at both ends of eaeh gear. .tiears with straight teeth also have the ohjei-tion that the teeth on a. pair of meshinggears engage with ear-h other along their toll length simnllaneonsly;with

consequent; shock, jar, and liability of break 11g and also with an objectionable noise or i'llLli'. litineover the shape of the teeth is such that only one or two teeth on one of the can be in Contact with the teeth on the other gear at the same time.

- 'ihe well-lmonni herringbone gear was clevis-ed in an attempt to secure a gear where the teeth mesh or engage progressively from end to end, thereby avoiding shock, jar, and the noisy click. in this gear the teeth are inelined spirally in on iosite directions from the median plane of the gear, but the gear has the objection that; when out or machined it cannot be fOllllGfl w'th teeth which are continuous and of fall eross section troin'encl to end. The ear can he cast. but, of course, is then only nt for a. limited duty. If the littering-hone gear nritle integral, with the teeth inclined spirally in both ,Clire ctions from the median plane, it is necessary to cu out a eertain portion of the metal where the oppositely inclined teeth nieet end to end in a median "plane, in order to provide clearance for the cutting tool. This has hereto fore onl; been obviated by forming the ear in right and left halves rigidly secured together, but the very fact that such gears are not integral mains them weaker at the median plane where the halvescontact. Herringbone have also been made with the oppositely inclined teeth stag 'ered with relation to each other at the me ianiplane, but here the teeth posed to make gears with teeth which are on red from end to Such gears,- however, have always had-the teeth of the same cross section from end to encl. In other words, they are what. may he known as twisted gears, and it has always been impossible to successfully machine or out the teeth of saehge-ars. 'llmy can be cast: but: not machined.

lily invention 1 of the deteets rel erren to and to provide a gear which can he sncessfnlly out or maohined: wherein, also the teeth are purposely made of varying shap from end to end in parallel cross seotionalplanes taken normal to the gear axis, and preferably so hat any will he stronger at the ends of the teeth than in the median plane, and Where, also, the press-tire angr e of the tooth Varies t. ilitt'erent points alon the length of the tooth.

lpgned to overcome all Patented Ring"; 12%, 1914.

are not Continuous from end to end ot the gear. it. has also been pro in my companion application, filed of even date herewith, Serial No. 758,967, I have described, illustrated and claimed a method of cutting gears, and the present invention relates particularly to the gear out according to the method specified in said application. it will, thereformbe unnecessary here to describe in detail the method of cutting: the gear.

As illustrated in the drawings, the gear comprises a body. 1 which is provided with a plurality of teeth 2 which, as illustrated in Fig. l, are curved or deviate circurnfen entially of" the gear, from end to end. tl'iereof. If the teeth of the near are considered as. developed upon a flat surface, in which case they will produce a rack, such, the rack lshown in Figs. 3 and 4, it will be found that the curvature of the teeth is in the arcs oil? circles, although they may be curved in other lines than circles. T he centers about which the arcs are st llCh' may be located in any plane transverse to the gear axis, for example, in a plane coinciding with the end face of the gear. "in this case the teeth will he gradually curved in only one direction, circmnferentially oi the gear, from one end to the'other. The radii about which the curves are struck may also vary, so that the degree of curvature and amount of deviation ol the teeth cireum'terentiallv of the gear may be increased or diminished. Preferably, the teeth are formed on curves struck about centers lying in the median trans verse plane of the gear, so that the teeth will be symmetrical with respect to said plane and deviate circuin'lf'erentially of the gear from end to end, first in one direction and then in the other. This produces a gear which in effect is a herringbone gear of modified type, and when two gears mesh, as illustrated in Fig. 5, the teeth thereof will mesh progressively from both ends to. ward the median plane, or vice versa. and

also exert an endwise thrust or wedging action upon each other. ll' hen the gear is symmetrical with respectto the median plane, this thrust will be exactly balanced in opposite diremions along; the axis and the gears will aecomnnalate themselves and remain in line with. eachothcr;

Fig. 2 re n'esents a section taken through the gear at the median plane, while Fig. 3 represents an end view of the gear. it will be seen that at the crests of the longitudinal curves in the teeth, the latter are formed with their side laces shaped to the proper lines of gear teeth, in the present case an involute tooth, and with a. given width at their tops and thickness at their bases. To-

ward the ends the teeth loeco ne gradually narrower at their tops and thicker at their bases, in planes normal to the gear axis, due to the particular method of cutting the teeth,

referred to. The thickness of the tooth at of th curve.

the pitch line, measured in lines transverse to the gear axis is, however, the same from end to end of the tooth. This amounts in effect to "a removal of some of the metal from the tops of the teeth at their ends to the bases of the teeth, thereby concentratinp, the metal in the end portions oi the teeth nearer to the axis of the gear and strengthening the ends of the teeth. This efl ect becomes more pronounced at increasing" distances from the crest of the tooth, or in the form shown, toward the ends of the teeth. The bottoms of the grooves between teeth become narrower and the top portions of the grooves wider toward the ends of the teeth.

in the particular form shown in the drawings, the teeth are of what is known as the involute type and are out by the gei'ieratingr action oi? two cutters and 1/, shown in l ip's. 6 and 7, the inclined edges 10 and 11 ()l' which are inclined in straight lines to an axis about which said cutters rotate. These inclined cutting edges l and Lil correspond to the side edges of what might be termed the normal rack tooth. It not essential, however, that the cutters used to form the gear be provided with cutting edges inclined on straight lines. The out tors may be oi the shape illustrated in 8 and that is, with their cutting ll) and curved or of special shape. Such cutters will generate a tooth of a different cross sectional shape from that shown in Figs. 2 and 3. lt will be understood, how ever,'that in any caselthe shape of the teeth will vary progressively from end to end.

hi l. 3 shows one of my improved gears meshing with a rack l. 'lhis rack has its teeth all in the same flat plane, and is praclically nothing more than the development of the teeth of the gear 1 upon said plane. in this connection it is, of course, to he on derslcod, that the invention is not limited to cylindrical gears, but is also applicable lo rachs ol the type shown, and also to bevel gears, and that in the claims the Word gear] is considered to include any fOl'Iii of toothed member, such as a spur gear, hevel gear or rack.

in use, the gears may he rotalcd in either direction. VVheu rolalcd in one dil'cttlion. the teeth come successively into engagement and first contact at their extrel'ne out-e1. ends a, the contact gradually advancing progressively in both directions toward the crest H the teeth are struck with radii sullicicntly short in proportion to the .diameter of the ear. and the cars are lon a 7'3 enough, the ends of the teeth may have passed out of contact beiliore'contact is reached at the crest 1). Moreover, for the same reason, different portions of two, three,

or more teeth may he in contact at the same time.

1 Oil all at the top, shown in Fig.

The gear described has the important advantage that a pair of the gears, or a gear and rack, will mesh or run substantially truly with each other, even if the axes of, the shafts are slightly inclined to each other, such as sometimes occurs when the two shafts are installed with poor alinement, or

in use get out of alinenient. In this case the as the axes of the gears become more and more inclined to each other the teeth do not mesh with or roll on each other so perfectly. In other words, the inclination of the gear axes to each other could not be carried too far. However, within reasonable limits, the gears will roll o mesh with each other truly and the very slight variation from perfect meshing is soon counteracted by the wear of the teeth, during which the shape themselves to each other. The gears have tlie capacity of correcting any usual errors due to shaft misalinenient. The geardescribed has also another important advantage in that the pressure angle of the. tooth is different at different points along the tooth. The pressure angle of the tooth is the angle or direction or". application of power from one gear to the other and is determined by the angle of inclination of the cutting edges of the generating cutter. As described in my copending application referred to, the effective angle of inclination or" the cutter varies along the tooth being formed, thereby producing the variation in the shape of the tooth above described. it also produces a variation in the pressure angle. as the tooth section shown in Fig. 2 which is a section in the median plane of the gear, is differenttroni the shape of tooth shown in Fig. 3, which is an end icw of the gear. The tooth which is broader at the base and narrower 3. has the greater pressure angle. and in tin. present the pressure angle at the median plane is substantially 20. while at the ends or" the gear the pressure angle 29. This gives an average pressure angle along the full length of the gear of about 241*.

What I claim is;

.1. A gear having teeth which extend longitudinally of the gear axis and which teeth are of varying cross section in parallel planes from end to end.

.2. A gear having teeth which car end longitudinally of the gear axis, said teeth being wider at. their bases at the ends of the teeth than in the median transverse plane of the gear.

3. A gear having teeth which extend longitudinally of the gear axis, said teeth being wider at their bases and narrower at their tops at the ends of the teeth than in the median transverse plane of the gear.

4.. A gear having continuous teeth deviating circumferentially of the gear from a straight line parallel with the axis of the gear, the cross section of the tooth in parallcl planes varying from end to end thereof.

5. Agear having continuous teeth deviating in both directions circuinferentially of the gear from a straight line parallel with the axis thereof, the cross section of the tooth in parallel planes varying from end to end.

6. A gear having continuous teeth extending from end to end thereof, said teeth be ing curved and having a varying cross section in parallel planes from end to end.

7. A gear haviiig continuous teeth extending from end to end thereof. said teeth being curved on the arcs of circles and of varying cross section in parallel planes from end to end.

8. A gear hating continuous teeth extend.- ing from end to end thereof, said teeth being curved on the arcs of circles and of varying cross section in parallel planes from end to end, said gear being symmetrical with ro-,

spect to its median transverse plane.

9. A toothed member provided with curved teeth which vary in cross section planes from end to end.

10. A toothed member provided with continuous teeth which are curved from end to end and symmetrical with respect to the :nc. dian plane of the member, said teeth being ot'varying cross section in parallel planes from end to end.

11. A gear hating teeth which extend longitudinally of the gear axis. said teeth being. narrower at their tops in parallel transverse planes at the ends of the teeth than-in the median transverse plane of the In testimony whereof, I have hereunto setiny hand.

in parallel Witnesses Ennna'r L. l lrnn, Jon): W. Tenn. 

